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https://issues.apache.org/jira/browse/MAHOUT-181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764369#action_12764369
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Grant Ingersoll commented on MAHOUT-181:
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Jake, can you bring this patch up to date? I'm getting errors on the applying
it to the test.
Thanks,
Grant
> DistanceMeasure is broken: iteration is done over nonZeroElements of
> v1.plus(v2), not v1.minus(v2)
> --------------------------------------------------------------------------------------------------
>
> Key: MAHOUT-181
> URL: https://issues.apache.org/jira/browse/MAHOUT-181
> Project: Mahout
> Issue Type: Bug
> Components: Matrix
> Affects Versions: 0.2
> Environment: all
> Reporter: Jake Mannix
> Assignee: Grant Ingersoll
> Fix For: 0.2
>
> Attachments: MAHOUT-181.patch
>
>
> SquaredEuclideanDistanceMeasure iterates over v1.plus(v2), which has the
> right number of nonzero elements if v1.get(i) != -v2.get(i) for all i
> indexing nonzero elements, but for example, the simple case of looking at
> SquaredEuclideanDisanceMeasure.distance(v, v.assign(new NegateFunction()))
> yeilds zero on current trunk, instead of 4*v.lengthSquared().
> Attached is a patch with a unit test which checks that
> DistanceMeasure.distance always returns nonnegative results and in particular
> also does not return , as well as a fix for ManhattanDistanceMeasure,
> SquaredEuclideanDistanceMeasure, and EuclideanDistanceMeasure.
> Unfortunately, the attached unit test reveals that the
> TanimotoDistanceMeasure is more broken than I can fix at present. It doesn't
> appear to be properly using the referenced formula in wikipedia, and in fact
> sometimes returns negative results. This means that with this patch applied,
> TestTanimotoDistanceMeasure is failing (and rightfully so).
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